Steve Bosshard wrote:
>
>> Unless the problem ISN'T two signals occupying the same spectrum, and
>> it's just a matter of one receiver hearing outside its 'channel'.
>>
>> Joe M.
>
> 146R325 occupies from 146315 to 146.335
> 146.310 occupies from 146.300 to 146.320
>
> They SHARE 146.315 to 146.320.
Oh Really? If you ASSUME (and you know how I mean that word) that each
TX HAS to have 20 kHz of bandwidth, I guess so, but that's not
necessary. Only if you have 5 kHz deviation and a 5 kHz of frequency
response (or some equivalent combination) will that be true. Most
radios, including ham radios, tend to have lower response, and many,
especially if set up correctly, will have less than 5 kHz of deviation.
In reality, each will have closer to 3 kHz response and 4.5 kHz of
deviation. That adds up to about 15 kHz of bandwidth, and ZERO
overlapping. IOW:
146R325 occupies from 146.3175 to 146.3325
146.310 occupies from 146.3025 to 146.3175
They SHARE... NOTHING!
Now, if your RECEIVER is passing 146.315 to 146.335, yes EXPECT
problems, as your OWN RECEIVER is causing the problem. I tend to think
that's the problem in this case. Of course, it could be users with TXs
that are too wide, too.
> The front end will make NO difference. Unless you have a VHF Crystal
> Filter ahead of the receiver input, and I doubt that would make any
> difference.
That must be why people with Micors and MASTR IIs have had fewer
problems except for very strong signals or users without properly set up
radios. ;-> They must be liars.
> Go narrow band and change IF filters and reduce modulation on BOTH
> systems, or QSY.
Well, if you're answer is either all or nothing, I guess so. BUT, there
is such a thing as GRAY areas where it doesn't have to be all of one or
none of it. Just because a radio CAN do 7 kHz deviation doesn't follow
that it MUST do 7 kHz deviation. Most people gave that mentality up when
they left CB. ("Only 100% modulation? Crank it up!!!")
You CAN limit your NFM deviation (modulation) and frequency response to
get adequate rejection without going overboard to SNFM. Of course, this
won't matter if your front end is wide as an elephant, which seems to be
the case here. Even IF you would go to SNFM, if your front end is
passing the RF energy that's contained in the adjacent channel's
passband, the problem will still exist.
I bet the Micor solves most of, if not all of the problem. Of course, it
will have done it via the methods I mentioned above and if the user
limits it to 4.0 kHz user audio + 0.5 kHz CTCSS deviation. Of course, it
won't matter how wide his TX is, as it's the RX that has the problem,
but to be a good neighbor and solve the problem for the users, it should
be set up this way.
Joe M.
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